(1) Field of the Invention
The present invention relates to a method and system for controlling fuel supplied to an internal combustion engine coupled with a supercharger. More particularly, the invention relates to a technology for eliminating any imprecision in an amount of fuel supplied due to an error in the detection of an intake air flow rate in an engine coupled with a supercharger.
(2) Related Art of the Invention
In electronic control systems for controlling an amount of fuel supplied to an internal combustion engine, usually a basic fuel supply amount Tp is calculated on the basis of an intake air flow rate Q detected by an air flow meter and an engine revolution speed N, and to control a supply of fuel to the engine based on the basic fuel supply amount Tp. (see Japanese Unexamined Patent Publication (kokai) No. 58-150040 and Japanese Unexamined Patent Publication No. 59-49334)
When the air flow rate Q is measured by an air flow meter and the engine is associated with a supercharger, such as turbocharger, mechanicalcharger and the like for boosting induction air, however, the following problems can arise.
In an internal combustion engine coupled with the supercharger, boosted air is abruptly shut off by a throttle valve during deceleration, to abruptly increase the pressure in a boost chamber between a compressor of the supercharger and the throttle valve, and due to this increased pressure in the boost chamber, the induction air can be directed to upstream of the compressor.
When a hot wire type air flow meter, such as that disclosed in Japanese Unexamined Utility Model Publication (Kokai) 1-171323 is used for measuring the intake air flow rate, the measured air flow rate tends to become much greater than that actually introduced, as such a type of air flow meter measures the air flow as a positive value, regardless of the air flow direction, and this results in a supply of an excess amount of fuel and a consequent overrich air/fuel ratio.